1. Field of the Invention
The invention described and claimed herein is generally related to electric light filaments, and more particularly to materials used as such filaments.
2. Description of the related art.
Previously known electric light filaments are typically made of materials which are either polycrystalline in nature or which are amorphous, or noncrystalline, in nature. Such materials suffer from the disadvantage that they become brittle with time at elevated temperatures.
Polycrystalline materials, which include the majority of commercially available metallic filaments, are characterized by the presence of crystal grain boundaries, dislocations, voids and various other microstructural imperfections. These microstructural imperfections lead to grain growth and recrystallization, particularly at elevated temperatures, which in turn lead to increased brittleness and diminished strength.
Metallic filaments also suffer from a disadvantage that is a consequence of the relatively low electrical resistance that characterizes metallic filaments. The low electrical resistance requires that the filaments be made quite long, which in turn requires the filament to be tightly coiled in order to fit it into a light bulb of suitable size. Coiling of the filament effectively reduces the radiating surface area because the coiled filament partially occludes itself, thereby diminishing the radiative efficiency of the filament.
Another disadvantage of metallic filaments is that metals in general, and particularly tungsten, have a relatively high resistivity/temperature coefficient. From room temperatures to approximately 1200.degree. C. the resistance of metal filaments increases as much a six-fold, resulting in high electrical power consumption at operating temperatures.
Amorphous metals used as filaments undergo various degrees of crystallization at elevated temperatures, resulting in the development of grain boundaries that decrease the strength and toughness of these materials also. Additionally amorphous materials are often of lower strengths initially relative to crystalline materials.
Accordingly, it an object and purpose of the present invention to provide an electric light filament which is of improved strength, durability and resilience, particularly at elevated temperatures.
It is also an object and purpose of the present invention to provide an electric light filament which does not undergo progressive crystallization or recrystallization at incandescent temperatures.